Predicting Micro-catchment Ponded Infiltration Dynamics

Rainfall and concentrated flow experiments were carried out on seven micro-catchments (MCs) that were designed to represent a rangeland restoration strategy using the Vallerani Plow. Prediction of infiltration rates within catchments is necessary to quantify potential benefits of restoration in a modeling framework. 3-D models of MC geometry and continuous stage measurements were used to calculate infiltration rates from field data. Soil samples and Guelph Permeameter (GP) measurements were collected to parameterize a predictive infiltration model. A 2-D simplified cross-section was developed to represent the MCs in Hydrus 2D/3D. The model domain was set up to mimic field simulations, and allowed for rainfall, evaporation, and time-varying ponded water levels. The antecedent rainfall and ponded water levels that were specific to each MC were applied in Hydrus models over a 400-minute simulation. Predicted velocity of water across the catchment boundary was averaged by depth intervals and multiplied against the surface area of that interval to calculate a volumetric flow rate. The soil at the field site had highly variable conductivity, both vertically within the soil profile and between sites. Consequently, four separate models of changes in conductivity with depth were evaluated, resulting in 28 total model runs. Model results were compared to measured infiltration data for six time intervals after the catchment was filled and began draining. The magnitude of predicted volumetric flow rates was highly variable and dependent on the Ks profile used. Use of the maximum field measured conductivity in the Hydrus model provided the best results, though it underpredicted measured flow rates by an average of 12%. Underprediction is likely due to preferential pathways that are not considered in the uniform flow model, the small size of GP measurements relative to the MC and use of a 2-D model to represent 3-D flow. Many opportunities exist to expand the modeling approach to test hypotheses on rangeland erosion and infiltration dynamics, and to develop optimal configurations of MCs at sites being considered for mitigation